A conventional fuel injection pump applied to an accumulator fuel injection system for a diesel engine is disclosed in JP-A-2000-240531.
The fuel injection pump disclosed in JP-A-2000-240531 includes a low-pressure pump portion, a fuel pressure regulating valve (return valve), and a high-pressure pump portion. The low-pressure pump portion (feed pump portion) pumps fuel from a fuel tank. The fuel pressure regulating valve (return valve) regulates pressure of fuel discharged from the feed pump portion. The high-pressure pump portion further pressurizes fuel, which is discharged from the feed pump portion, and press-feeds the fuel to a common rail, which stores the fuel at high-pressure.
The return valve opens and returns fuel from the downstream of the feed pump portion to the upstream of the feed pump portion when pressure of fuel discharged from the feed pump portion becomes greater than predetermined pressure. The return valve is inserted to a mounting hole (mounting portion) provided in a pump housing as an outer shell of the fuel injection pump, thereby the return valve is mounted to the fuel injection pump.
However, the pump housing of the fuel injection pump disclosed in JP-A-2000-240531 includes the high-pressure pump portion and the feed pump portion. The pump housing is formed with multiple fuel passages and a mounting portion to which a component such as the feed pump portion is mounted. Therefore, interference between fuel passages and the mounting hole, in which the return valve in pump housing is inserted, needs to be avoided when the mounting hole is formed. Accordingly, manufacturing of the mounting hole is complicated.
In view of the present problem, the present inventor filed the Japanese patent application No. 2007-21378 to propose a structure in which the mounting hole, to which the return valve is inserted, is formed in the feed pump cover (low-pressure pump cover), which is a separate component from the pump housing. In the present structure of the fuel injection pump, workability of the mounting hole is enhanced compared with JP-A-2000-240531 in which the mounting hole is formed in the pump housing.
The low-pressure pump cover functions as an outer shell of the feed pump portion. The low-pressure pump cover is fixed to the pump housing by using a bolt or the like while accommodating a rotatable member of the feed pump portion. Specifically, a trochoid rotor of a trochoid pump as the feed pump portion is accommodated in the low-pressure pump cover.
In short, the low-pressure pump cover functions as a part of the feed pump portion. In addition, the low-pressure pump cover also functions as a mounting member used for mounting the feed pump portion to the pump housing. The low-pressure pump cover accommodates the rotatable member of the feed pump. Therefore, high dimensional accuracy of, for example, tens of microns is required to the low-pressure pump cover when the inside of the low-pressure pump cover is manufactured.
Therefore, the outline of the low-pressure pump cover may be complicated for being chucked when the inside of the low-pressure pump is manufactured. Moreover, when the mounting hole, to which the return valve is inserted, is formed after manufacturing the inside of the low-pressure pump cover with high accuracy, the inside of the low-pressure pump cover may be deformed. Accordingly, in the fuel injection pump according to the Japanese patent application No. 2007-21378, workability of the mounting hole may not be sufficiently enhanced.